Most blood pumps used in open heart surgery or for auxiliary circulation have been constant flow rate pumps exemplified by a roller pump. The roller pump structurally delivers blood in such a way that rotating rollers compress a tube through which blood flows, which thus causes safety problems such as a great loss of blood cells and a risk of foreign material entrainment due to tubing wear.
Given this background, in recent years, a centrifugal pump replacing the roller pump has been increasingly used. The centrifugal pump offers a variety of advantages compared to the roller pump, such as no occurrence of dangerous high pressure, a high level of safety against air entrainment, and no generation of excessive negative pressure.
However, even when the centrifugal pump operates at a constant rotational frequency, the centrifugal pump can cause a blood supply flow rate to be changed upon variation of pressure loading due to narrowing of the patient's blood vessels. An additional flowmeter for sequentially monitoring the blood supply flow rate is thus required to be provided. Also, attempts have been made to keep the blood supply flow rate constant by controlling an arterial line occluder (see, for example, Patent Literature 1) or by controlling the rotational frequency of the centrifugal pump (see, for example, Patent Literatures 2 and 3) under constant monitoring of the flowmeter. As such a flowmeter, an ultrasonic flowmeter or an electromagnetic flowmeter can be used.